Intimate mixture or alloy



Patented Nov. 14, 1%33 hurrah snares earner or ies mrnna'rn tnxrons onerror York No Drawing. application July 22, 1930, Serial No. 460,913.Renewed January 31, 11933 3 Claims.

This invention relates to non-tarnishing metallic mixtures and alloys. I

It is an object of the invention to produce an intimate metallic mixtureor alloy which is tar- Irish-resisting and has a pleasant color.

An appreciable amount of indium added to silver produces an intimatemixture or alloy which has tarnish-resisting properties due to theindium. The indium, however, imparts a bluish tint or color to thesilver and such color is considered objectionable particularly where thealloy is employed as a finish plating.

We have discovered that the addition of a third metal to the alloyproduces an improvement in color and an intimate mixture of theelements. When the alloy or-intimate mixture is used as a plating, itcan be produced advantageously by plating the elements in superposedlayers in elternate fashion and difl'using. While the elements may beplated individually or singly, in the present most advantageouspractise, two of the elements are plated simultaneously from a platingbath, then the third metal is plated and finally by diffusing the platedlayers there is produced an alloy or intimate mixture of the metals.

While various metals may be associated in the intimate mixture or alloyof the present invention, one advantageous combination is silver, goldand indium. In this alloy, the gold color counteracts the indium colorand the alloy color simulates that of silver. This alloy may be producedby plating and, in the present preferred practise, the silver and goldare simultaneously plated from the same bath, the indium then platedthereon and the metals caused to mix intimately or alloy by diffusing.

In the simultaneous gold-silver plating, the anode of the bath is analloy of gold and'silver and the cathode is the base metal, such asnickel silver or even solid silver, to be plated simultaneously by thegold and silver. While the proportions of the metals in the anode mayvary, as an example, the anode may contain i2 gold and El /2% silver.The bath is advantageously a cyanide hath containing 8 ounces or. moreof free potassium cyanide salt per gallon, 0.6 to 1.0 ounces of gold inthe form. of a cyanide salt per gallon, and approximately 3.0 ounces ofsilver in the form of cyanide salt. Foe current density during theplating process is about 1/14 ampere per square inch. Under normal roomtemperatures, the process produces a good commercial plate containingabout 12 /2% gold and 87 silver.

The plating of indium on the gold-silver plate and when all the layershave been plated, to

fuse for a suitable length of time, and at a s'ifit able temperaturewhereby the metals of the layers intimately mix or alloy into ahomogeneous single layer.

In carrying out the process in its entirety, the

-base metal, such as nickel silver, is first thorough- 1y cleaned. Athorough cleaning of the base involves successive application of anumber of cleaning steps which are Well known. An advantageous cleaningis obtained by subjecting the base metal to the following:

( 1) Hot boiling soap solution.

(2) Hot water rinse.

(3) Hot mineral cleaner.

(4) Cold running water rinse.

(5) Alkali electric, cleaner.

(6) Cold running water rinse.

(7) Dilute hydrochloric acid clip.

(3) Cold running water rinse.

After this treatment, a very thin plate of nickel may be applied in anysuitable manner and the base again subjected to a cold running waterrinse.

The base is now advantageously subjected to a. silver strike for about 8seconds in a solution containingabout ounces of silver per gallon in theform of potassium salts and 9 or 10 ounces of free potassium cyanide.This treatment produces a very thin silver layer on the base surface,giving a silver interior surface, and conditions said surface for theapplication of the heavier gold-silver and indium plates.

The gold-silver plating is now applied to about 25 millionths of an inch(0.000025) and the article then rinsed in cold water. It is thensubjected to treatment in the indium bath to obtain an indium. layer ofabout 20 millionths of an inch (0.000020). At this point, a. very thinlayer of silver and indiurn may advantageously be applied and, in onepractical method, the result is accomplished by a strike in a bathcontaining ounces of silver per gallon in the form of cyanide salts,about 1 110 C. for about 8 hours.

.not necessarily desired.

ounce of indium per gallon in the form of cyanide salts, about ounce ofdextrose and about 10 ounces of free potassium cyanide per gallon. Thecurrent density is about ampere per square inch for a short time.

The article is now subjected. to another goldsilver plating to about0.000025 inches and, following this; may be subjected to successiveplatlngs of indium and gold-silver with the intermediate silver indiumstrikes and rinses until the desired thickness of plate has been builtup. The application of successive steps for about ten (10) times hasbeen found to give satisfactory results.

After the successive platings as above outlined, the produce issubjected to a diffusing process to cause the metals to alloy or mixintimately. The diffusion of the indium occurs at or about its meltingpoint. The diffusing process is most advantageously carried out in twosteps, the first step being a seasoning or readjustment to start thediiiusion between the layers and the second step the complete diffusionof the layers together. In one practical species of the process, thefirst step is carried on with a preliminary heating at The second isperformed in an oven at 165 C. for about 18 hours. In this way, a verysatisfactory homogeneous plate is produced.

With the compositions and thicknesses discussed, the final coatingcontains about 36% indium, 8/z% gold and silver. These ratios may bevaried as desired by changes in the original compositions andthicknesses.

This surface alloy is non-tarnishing and has a color simulating puresilver. It may be applied to base metals of various kinds and may beapplied to silver itself, for example, to impart preservative surfacecoatings to precious silver articles.

In lieu of plating the silver and gold simultaneously and the indiumseparately, the silver and indium may be plated simultaneously, forexample, by a bath such as described or otherwise, and the gold platedseparately, the layers being built up alternately and the metals thenintimately mixed or alloyed by diffusion.

Metals other than gold might be employed to modify the objectionableindium color and to give a more pleasing color where real silver coloris By way of example, an alloy may be of silver, palladium and indiumand produced by plating the silver and palladium simultaneously and theindium separately in alternate superposed layers and then diffusing.

A suitable palladium-silver plating bath is as follows:---

Ounces per gallon Palladium (in cyanide) 0. 8 Potassium cyanide (free)5. 0 Potassium carbonate 5. 0 Potassium nitrate 1. 0 Silver 1. 0

The plating occurs with very little agitation at a current density ofabout 0.1 ampere per square inch. It is likely that, by having a muchlarger.

taneously and the indium separately in alternate layers and thendiiiusing.

A suitable cadmium-silver plating bath is as follows:-

Ounces per gallon Cadmium 0.8 Silver 2.4 Potassium cyanide 2. 4

silver, copper and indium and may be produced by plating the silver andcopper simultaneously and the indium separately in alternate layers andthen difiusing.

To obtain a suitable copper-silver bath, 250 grams of copper cyanide aremixed with 300 grams of potassium cyanide and 500 cubic centimeters ofwater added and the mixture stirred until the maximum amount of coppercyanide is dissolved. The solution is filtered and made up to twoliters. The solution is a clear, light amber colored liquid, from which,when cold, a small quantity of white crystalline material isprecipitated. This precipitate is the double cyanide oi copper andpotassium and dissolves when the solut'on is warmed. To this solution,silver is added in the form of silver potasium cyanide with a slightexcess of potassium cyanide. The added solution is prepared by mixing 50grams of silver cyanide and 50 grams of potassium cyanide and addingenough water to give 375 cubic centimeters solution. The aboveingredients can probably be varied within wide limits, but the examplegiven has been found to give good deposits.

It 'will be noted that silver, gold and copper are in the same group andsub-group of the periodic system, viz: group 1 sub-group, or family, B,so that gold and copper may be designated generically as metals otherthan silver of the same group and sub-group as silver.

What is claimed is:

l. A non-tarnishing intimate mixture or alloy having a color simulatingsilver comprising indium, gold and silver substantially in the ratio ofabout 36% indium, ii gold and 55 silver.

2. A non-tarnishing mixture or alloy consisting of silver, indium and acolor-modifying metal selected from the group consisting of gold,palladium, cadmium, and copper, the silver constituting more than 50% byweight of the total alloy, the indium and the color-modifying metalconstituting substantially the entire remainder,

